Method for manufacturing a member for purifying automobile exhaust gas

ABSTRACT

A method for manufacturing a member for purifying exhaust gas for an automobile exhaust line, including an enclosure, an exhaust gas purification unit arranged in the enclosure, and at least one element for supporting the unit. The method includes the following steps:
         obtaining a first quantity representative of a mass (Mb) of the exhaust gas purification unit;   using at least the first quantity obtained, determining an installation density (d mounted ) of the or each support element;   determining at least one diameter (Denclosure) of the enclosure as a function of the determined installation density (d mounted ) ;   assembling the enclosure, the support element(s) and the gas purification unit, so as to obtain the diameter that was determined for the enclosure and the installation density (d mounted ) that was determined for the support element(s).

Method for manufacturing a member for purifying automobile exhaust gasThe present invention generally concerns methods for manufacturingmembers for purifying automobile exhaust gas.

More specifically, the invention concerns a method for manufacturing amember for purifying exhaust gas for an automobile exhaust line, thepurification member comprising a substantially cylindrical enclosuredefining a circulation channel for the exhaust gas, a substantiallycylindrical exhaust gas purification unit arranged in the enclosure, andat least one element for supporting the exhaust gas purification unit,the exhaust gas purification unit having a side wall turned toward theenclosure and defining an annular space with said enclosure, the or eachsupport element being inserted into the annular space between theenclosure and the side wall of the exhaust gas purification unit.

U.S. Pat. No. 6,389,693 describes a manufacturing method comprising astep for measuring the diameter of the gas purification unit, a step formeasuring the mass of the support element, and a step for calculatingthe diameter of the enclosure as a function of the measurements done.

In certain purification members obtained using this method, the exhaustgas purification unit is not completely supported inside the enclosure.

In this context, the invention aims to propose a manufacturing methodthat is even more precise.

To that end, the invention concerns a method for manufacturing apurification member of the aforementioned type, characterized in that itcomprises the following steps:

-   -   obtaining a first quantity representative of a mass of the        exhaust gas purification unit;    -   using at least the first quantity obtained, determining an        installation density of the or each support element in the        annular space;    -   determining at least one diameter of the enclosure as a function        of the determined installation density;    -   assembling the enclosure, the support element(s) and the gas        purification unit, so as to obtain the diameter that was        determined for the enclosure and the installation density that        was determined for the support element(s).

The method can also include one or several of the features below,considered individually or according to all technically possiblecombinations.

The installation density (d_(mounted)) is determined by calculating astress (F) applied to the gas purification unit from the first quantityobtained and determining the installation density (d_(mounted)) from thecalculated stress (F).

The installation density (d_(mounted)) is determined from the stress (F)calculated using predetermined mappings.

The method also comprises a step for obtaining a third quantity (Db)representative of the diameter of the gas purification unit, thediameter of the enclosure (Denclosure) also being determined as afunction of the third obtained quantity (Db).

The method also comprises the following steps:

-   -   obtaining a second quantity representative of the mass (Mb) of        the or each support element;    -   using the second quantity (Mn), determining the initial surface        density (MSin) of the or each support element before        installation;    -   determining a thickness value (e) of the annular space as a        function of the determined surface density (MSin);        the diameter (Denclosure) of the enclosure also being determined        as a function of the determined thickness value (e).

The thickness value (e) is calculated as a function of the ratio betweenthe determined surface density (MSin) and the determined installationdensity (d_(mounted)).

The enclosure, the support element(s) and the exhaust gas purificationunit are assembled using the following steps:

-   -   arranging the support element(s) around the exhaust gas        purification unit;    -   inserting the support element(s) and the exhaust gas        purification unit into the enclosure, so as to obtain a        provisional diameter of the enclosure larger than the determined        diameter (Denclosure) and a provisional installation density for        the support element(s) lower than the determined installation        density (d_(mounted));    -   reducing the enclosure to the determined diameter (Denclosure),        the support element(s) then being at the determined installation        density (d_(mounted)).

The insertion step is carried out by inserting the support element(s)and the exhaust gas purification unit into the enclosure forcibly, or byrolling the enclosure around the support element(s).

The enclosure, the support element(s) and the exhaust gas purificationunit are assembled using the following steps:

-   -   arranging the support element(s) around the gas purification        unit;    -   inserting the support element(s) and the exhaust gas        purification unit into the enclosure, so as to directly obtain        the determined diameter (Denclosure) for the enclosure and the        determined installation density (d_(mounted)) for the support        element(s).

The exhaust gas purification unit is a particle filter of a catalyticpurification member.

Other features and advantages of the invention will emerge from thedetailed description thereof provided below, for information andnon-limitingly, in reference to the appended figures, in which:

FIG. 1 is a longitudinal cross-sectional view of a purification membermanufactured using the method according to the invention;

FIG. 2 is a diagram showing the steps of the method according to theinvention making it possible to determine the diameter of the enclosureto be manufactured;

FIGS. 3 to 6 are diagrammatic views illustrating the different steps ofassembling the purification member.

The exhaust gas purification member 1 illustrated in FIG. 1 is intendedto be inserted in an automobile exhaust line (not shown). It includes asubstantially cylindrical enclosure 3, a substantially cylindricalexhaust gas purification unit 5 and a supporting lap 7 for the gaspurification unit. The enclosure 3 is a metal enclosure provided to beconnected toward the upstream direction of the exhaust line to adivergent cone defining an exhaust gas inlet, and toward the downstreamdirection a convergent cone defining an exhaust gas outlet. The inlet isconnected to the manifold of the exhaust line, which captures theexhaust gas coming out of the combustion chambers of the engine. Theoutlet is connected to the cannula through which the exhaust gas isreleased into the atmosphere after purification.

Upstream and downstream here are used in relation to the normaldirection of circulation of the exhaust gas.

The unit 5 is typically a particle filter or a catalytic purificationmember. A catalytic purification member is typically made up of agas-permeable structure covered with catalytic metals favoring oxidationof the combustible gases and/or reduction of the nitrogen oxides.

A particle filter is made of a filtration material made up of amonolithic structure made of ceramic or silicon carbide havingsufficient porosity to allow the passage of the exhaust gases. However,as is known in itself, the diameter of the pores is chosen small enoughto ensure retention of the particles, and in particular soot particles,on the upstream face of the filter. The particle filter can also be madeup of a cartridge filter or a sintered metal filter.

The particle filter used here for example includes a set of parallelducts distributed into a first group of inlet ducts and a second groupof outlet ducts. The inlet and outlet ducts are arranged in staggeredrows.

The inlet ducts emerge on the upstream section of the particle filterand are covered at the downstream section of the particle filter.

On the contrary, the outlet channels are covered over the upstreamsection of the particle filter and emerge on its downstream section.

The enclosure 3 and the gas purification unit 5 are substantiallycoaxial, this axis being noted X in FIG. 1. The unit 5 has a reduceddiameter in relation to the enclosure 3. It is defined by a side wall 9turned toward the enclosure 3 and defining an annular space 11 with theenclosure 3.

The support lap 7 is arranged in the annular space 11. It is insertedbetween an inner face 13 of the enclosure and the side wall 9 of the gaspurification unit. It extends over the majority of the axial length ofthe unit 5.

The enclosure 3 therefore inwardly defines a passage for circulation ofthe exhaust gas from the inlet to the outlet through the ceramicmaterial unit 5. The exhaust gases are purified as they pass through theunit 5.

The lap 7 is for example made of an intumescent material. The lap can beof the XPEAV2 type sold by the company UNIFRAX or for example the typesold under the name NEXTEL SAFFIL or 3M, or the type sold under the nameCC-MAX or FIBERMAX by the company UNIFRAX.

The lap 7 bears outwardly on the enclosure 3 and bears inwardly on theunit 5. It therefore exerts radial pressure on the unit 5. The lap 7contributes to keeping the unit 5 in position when the latter issubjected to a longitudinal stress parallel to the axis X, and also whenthe latter is subjected to a radial stress. When the unit 5 is subjectedto a longitudinal stress, the friction between the unit 5 and the lap 7and between the lap 7 and the enclosure 3 are such that the movement ofthe unit 5 in relation to the enclosure 3 is very limited.

To obtain this effect, it is necessary to install the lap 7 in theannular space 11 with a suitable installation density. Installationdensity refers to the density of the lap 7 at ambient temperature. Thisdensity must not be too low because the unit 5 would be poorly kept inposition in relation to the enclosure 3 under the effect of alongitudinal stress. This would be true in particular at hightemperatures, due to the differential expansion between the enclosure 3and the unit 5, which leads to an increase in the thickness of theannular space.

The installation density also must not be too high, to avoid damagingthe ceramic material unit, in particular in the long term.

The manufacturing method explained below takes these various constraintsinto account.

The method includes a first phase aiming to determine the diameter ofthe enclosure 3 of the purification member.

As shown in FIG. 2, to that end the method includes a step in which afirst quantity Mb representative of the mass of the gas purificationunit 5 is obtained, a step during which a second quantity Mnrepresentative of the mass of the lap 7 is obtained, and a step duringwhich a third quantity Db representative of the diameter of the gaspurification unit 5 is obtained.

The diameter Db for example corresponds to the average of severalexterior diameter measurements, done on different sections of the unit5. These sections are for example regularly axially spaced along theunit 5. The quantity Db can also correspond to the maximum of the valuesnoted at different points of the unit 5. The masses Mb and Mn are forexample directly measured using scales.

As shown in FIG. 2, the method includes a step during which the stress Fnecessary to keep the unit in position in relation to the enclosure 3 iscalculated. A longitudinal stress is considered here. The stress F canbe calculated using the following formula:

F=Mb g 9.81

where g is the longitudinal acceleration applied to the unit 5. Apredetermined acceleration g is used to calculate F. This accelerationfor example corresponds to the maximum acceleration undergone by theunit in standard life situations of the vehicle. These life situationsare for example standing start with strong acceleration, emergencybraking, or the impact of the vehicle against an obstacle at moderatespeed.

The installation density of the lap 7 between the unit 5 and theenclosure 3 is then determined, as a function of the stress F calculatedabove. The installation density is expressed in lap mass per volume unitof the annular space, at ambient temperature. The installation densityd_(mounted) is determined using predetermined mappings. These mappingscome from bench and/or road tests of the vehicle. They give the densityd_(mounted) as a function of the stress F for different types of lapsand different types of units.

The density of the lap before installation MSin is then determined.

The density of the lap before installation is a surface density. It isobtained by dividing the mass Mn of the lap by the area of the lap, thearea being considered under conditions where the lap is not compressedor stretched.

The thickness to be provided for the annular space 11 between the sidewall 9 of the unit and the inner face of the enclosure 13 is thendetermined. This thickness is calculated using the following formula:

e=MSin/d _(mounted)

where e is the thickness expressed in millimeters, MSin is expressed ingrams per square meter, and d_(mounted) is expressed in kilograms percubic meter.

The inner and/or outer diameter of the enclosure is then calculatedusing the following formulas.

Inner diameter: Denclosure=Db+2e

Outer diameter: D _(ext) =Db+2 e+2Ep

where Ep is the thickness of the enclosure 3. Ep is measured, or isprovided by the manufacturer of the enclosure.

During a second phase, illustrated in FIGS. 3 to 7, the enclosure, thelap, and the gas purification unit are assembled so as to obtain thedetermined diameter for the enclosure and the determined installationdensity for the lap.

In a first embodiment, an enclosure 3 is supplied with an inner diameterequal to the diameter Denclosure calculated as described above. The lap7 is first arranged around the ceramic unit 5. The lap and the unit arethen jointly inserted into the enclosure. For example, the lap and theunit are forcibly inserted into the enclosure 3, using a tube sinking 15and a piston 17. The tube sinking 15 comprises a substantiallyconvergent tapered inner channel 19. The end 21 of the channel 19 havinga small diameter has an inner diameter substantially equal to the innerdiameter of the enclosure 3. The enclosure 3 is placed next to and inthe extension of the end 21. It is locked in relation to the tubesinking 15 by a stop 23.

The unit 5 and the lap 7 are forced along the inner channel 19 from theend 25 having the larger diameter by the piston 17. The lap 7 isgradually compressed as the unit 5 and the lap 7 move along the innerchannel 19 and penetrate the enclosure 3 (FIG. 4). The piston 17 pushesthe lap 7 and the unit 5 until they are completely housed in theenclosure 3 (FIG. 5). For example, the stop 23 is used to limit thetravel of the unit 5 and the lap 7 and stop them in the desired positionin relation to the enclosure 3.

In another embodiment, an enclosure is supplied that has an innerdiameter slightly larger than the diameter Denclosure calculated asdescribed above. This alternative is described in U.S. Pat. No.6,389,693.

As before, the lap 7 is first arranged around the ceramic unit 5. Thelap and the gas purification unit are then inserted into the enclosure,for example using the tube sinking 15 and piston 17, according to theprocedure described in reference to FIGS. 3 to 5.

Once the lap is inserted, it has a provisional installation densitylower than the installation density d_(mounted) determined as describedabove. The enclosure has a provisional inner diameter larger than thediameter Denclosure determined according to the method above. Asillustrated in FIG. 6, the enclosure is then reduced to the determineddiameter

Denclosure, the lap being compressed at the same time to an installationdensity corresponding to the value d_(mounted) calculated above.

To that end, the purification member is placed in a cylindricalcompression tool 27, as illustrated in FIG. 6. The tool 27 includes aplurality of sectors 29 inwardly defining a cavity 31 in which thepurification member is placed. The sectors 29 are distributedcircumferentially, around the cavity 31. They are initially separatedfrom each other by circumferential interstices.

The tool 27 also includes means for urging the different sectors 29, ina controlled manner, radially toward the inside of the cavity. Thesectors 29 then bear on the outer surface of the enclosure 3 and willstress it until the enclosure has the outer diameter D_(ext) calculatedabove.

The above method has multiple advantages.

Because it comprises the following steps:

-   -   obtaining a first quantity representative of a mass of the        exhaust gas purification unit;    -   obtaining a second quantity representative of the mass of the or        each support element;    -   using the first and second obtained quantities, determining an        installation density of the or each support element in the        annular space;    -   determining at least one diameter of the enclosure as a function        of the determined installation density;    -   assembling the enclosure, the support element(s) and the exhaust        gas purification unit, so as to obtain the determined diameter        for the enclosure and the determined installation density for        the support element(s);

the method makes it possible to more precisely manufacture thepurification member. In particular, the diameter of the enclosure ismore precisely dimensioned.

When the manufacturing method takes measurements of the mass of the oreach support element, the mass of the gas purification unit and thediameter of the gas purification unit all into account, it makes itpossible to dimension the enclosure of the purification memberespecially precisely. This makes it possible, if applicable, to decreasethe thickness of the metal enclosure, and therefore to save material.

This also makes it possible to more accurately dimension the installeddensity of the support element(s) and thereby increase the longevity ofthose elements.

In certain cases, the method makes it possible to lower the installationdensity of the support element(s), and therefore to use elements havinga lower mass per surface unit, in the unstressed state.

Moreover, because the installation density of the support element(s) iswell controlled, the risks of damaging the gas purification unit overtime are reduced.

The insertion of the support elements and the unit inside the enclosureis better mastered, since the diameter of the enclosure is preciselydimensioned. In particular, this makes it possible to limit theamplitude of the reduction necessary to insert the support element(s)and the unit inside the enclosure.

For a ceramic unit with a more complex shape, the method can make itpossible to avoid using an erosion seal. In fact, the erosion dependsdirectly on the compression density of the lap. Strong erosion can beseen when the installation density is too low or too high. A betterestimate of the installation density therefore makes it possible todistance the system from densities at risk for erosion.

The method described above can have multiple alternatives.

In one non-preferred alternative, only the mass of the gas purificationunit is measured, and a predetermined diameter value for the unit and apredetermined mass value per surface unit for the lap are used todetermine the diameter of the enclosure.

The lap and the unit are not necessarily inserted into the enclosureusing a tube sinking. For example, the enclosure can be rolled aroundthe lap.

In the alternative where it is necessary to reduce the enclosure afterinsertion of the or each support element and the unit, this operationcan be done by passing the assembly formed by the unit, the supportelement(s) and the enclosure through a tube sinking having a taperedinner channel. This tube sinking is generally of the type illustrated inFIGS. 3 to 5.

The unit is not necessarily kept in place in the enclosure by a lap. Theunit can be kept in place by one or several seals, typically two sealsplaced at the two axial ends of the unit. The seals can be O-rings,placed around the units in the annular space separating the unit fromthe enclosure.

The seals can also be annular seals with L-shaped sections. Each sealhas a wing engaged around the unit in the annular space separating theunit and the enclosure. Each seal also includes another wing pressed ona frontal unit face perpendicular to the axis X. The seals can be madeof metal fibers and/or ceramic fibers.

The unit can also be kept in place both by a lap inserted between acentral axial section of the unit and the enclosure, and one or severalseals as described above, inserted between the axial ends of the unitsand the enclosure.

1. A method for manufacturing a member for purifying exhaust gas for anautomobile exhaust line, the purification member (1) comprising asubstantially cylindrical enclosure (3) defining a circulation channelfor the exhaust gas, a substantially cylindrical exhaust gaspurification unit (5) arranged in the enclosure (3), and at least oneelement (7) for supporting the exhaust gas purification unit (5), theexhaust gas purification unit (5) having a side wall (9) turned towardthe enclosure (3) and defining an annular space (11) with said enclosure(3), the or each support element (7) being inserted into the annularspace (11) between the enclosure (3) and the side wall (9) of theexhaust gas purification unit (5), the method being characterized inthat it comprises the following steps: obtaining a first quantityrepresentative of a mass (Mb) of the exhaust gas purification unit (5);using at least the first quantity obtained, determining an installationdensity (d_(mounted)) of the or each support element (7) in the annularspace (11); determining at least one diameter (Denclosure) of theenclosure (3) as a function of the determined installation density(d_(mounted)); assembling the enclosure (3), the support element(s) (7)and the gas purification unit (5), so as to obtain the diameter that wasdetermined for the enclosure (3) and the installation density(d_(mounted)) that was determined for the support element(s) (7).
 2. Themethod according to claim 1, characterized in that the installationdensity (d_(mounted)) is determined by calculating a stress (F) appliedto the gas purification unit (5) from the first quantity obtained anddetermining the installation density (d_(mounted)) from the calculatedstress (F).
 3. The method according to claim 2, characterized in thatthe installation density (d_(mounted)) is determined from the stress (F)calculated using predetermined mappings.
 4. The method according toclaim 1, characterized in that it also comprises a step for obtaining athird quantity (Db) representative of the diameter of the gaspurification unit (5), the diameter of the enclosure (Denclosure) alsobeing determined as a function of the third obtained quantity (Db). 5.The method according to claim 1, characterized in that it also comprisesthe following steps: obtaining a second quantity representative of themass (Mb) of the or each support element (7); using the second quantity(Mn), determining the initial surface density (MSin) of the or eachsupport element (7) before installation; determining a thickness value(e) of the annular space (11) as a function of the determined surfacedensity (MSin); the diameter (Denclosure) of the enclosure (3) alsobeing determined as a function of the determined thickness value (e). 6.The method according to claim 5, characterized in that the thicknessvalue (e) is calculated as a function of the ratio between thedetermined surface density (MSin) and the determined installationdensity (d_(mounted)).
 7. The method according to claim 1, characterizedin that the enclosure (3), the support element(s) (7) and the exhaustgas purification unit (5) are assembled using the following steps:arranging the support element(s) (7) around the exhaust gas purificationunit (5); inserting the support element(s) (7) and the exhaust gaspurification unit (5) into the enclosure (3), so as to obtain aprovisional diameter of the enclosure (3) larger than the determineddiameter (Denclosure) and a provisional installation density for thesupport element(s) (7) lower than the determined installation density(d_(mounted)) ; reducing the enclosure (3) to the determined diameter(Denclosure), the support element(s) (7) then being at the determinedinstallation density (d_(mounted)).
 8. The method according to claim 7,characterized in that the insertion step is carried out by inserting thesupport element(s) (7) and the exhaust gas purification unit (5) intothe enclosure (3) forcibly, or by rolling the enclosure (3) around thesupport element(s) (7).
 9. The method according to claim 1,characterized in that the enclosure (3), the support element(s) (7) andthe exhaust gas purification unit (5) are assembled using the followingsteps: arranging the support element(s) (7) around the gas purificationunit (5); inserting the support element(s) (7) and the exhaust gaspurification unit (5) into the enclosure (3), so as to directly obtainthe determined diameter (Denclosure) for the enclosure (3) and thedetermined installation density (d_(mounted)) for the support element(s)(7).
 10. The method according to claim 1, characterized in that theexhaust gas purification unit (5) is a particle filter of a catalyticpurification member.
 11. The method according to claim 1, characterizedin that the first quantity is obtained by measuring the mass (Mb) of theexhaust gas purification unit (5).
 12. The method according to claim 1,characterized in that it comprises a step for obtaining a secondquantity representative of the mass (Mn) of the or each support element(7), the installation density (d_(mounted)) of the or each supportelement (7) in the annular space (11) being determined using the firstand second obtained quantities.